Anisotropically conductive interconnection media have been proposed for establishing temporary or permanent electrical connections, e.g., between device contacts and corresponding contacts on a supporting substrate, thereby replacing solder connections or substituting for test probes. Such a medium typically is based on the use of a composite material which comprises electrically conducting elements in a nonconductive matrix material. Electrically conducting elements may take the form of wire segments as disclosed, e.g., in the following items:
U.S. Pat. No. 4,003,621, issued Jan. 18, 1977 to R. W. Lamp; R. L. Schelhorn, "Test Fixture for Testing Chip Carrier Devices Assembled in Larger Circuits", RCA Technical Notes, TN No. 1315, Oct. 12, 1982; and R. L. Schelhorn, "Universal Test Fixture for Testing Chip Carriers", RCA Technical Notes, TN No. 1316, Oct. 12, 1982.
Manufacture of a wire-based interconnection medium may involve cutting from a block as disclosed in U.S. Pat. No. 4,003,621 cited above; alternatively, and as disclosed in U.S. Pat. No. 4,209,481, issued June 24, 1980 to Y. Kashiro et al., manufacture may involve magnetic alignment of pre-cut wire segments in a layer of nonconductive material.
As an alternative to an interconnection medium including wire segments, interconnection media have been proposed in which spherical or near-spherical particles serve the function of bridging between surfaces; in this respect see, e.g., the following items:
U.S. Pat. No. 4,113,981, issued Sept. 12, 1978 to M. Fujita et al. and UK Patent Application GB 2,068,645 A, published Aug. 12, 1981 for W. Harper.
In yet another type of interconnection medium, anisotropic conductivity is due to particle chains between opposite surfaces of a layer or sheet medium, such chains providing for electrical interconnection across the thickness of the medium while contact points or pads on the same side of the medium remain insulated. While a statistical effect known as percolation may be effective to meet such requirements, alternate structures have been proposed in which desired chain formation is more positively imposed. In particular, particle alignment by magnetic means has been advocated.
This approach provides for alignment for magnetic particles into electrically conducting columnar chains upon application of a magnetic field in the direction of desired conduction; in this respect, see, e.g.,
V. E. Gul et al., "Investigation of Electrically Conducting Anisotropic Structures in Polymer Materials. Influence of a Magnetic Field on the Conductivity of Polymer Materials Containing Conductive Fillers", Kolloidnyi Zhurnal, Vol 30 (1968), pp. 13-18; U.S. Pat. No. 4,548,862, issued Oct. 22, 1985 to R. B. Hartman; and U.S. patent application Ser. No. 728,813, filed Apr. 30, 1985, now U.S. Pat. No. 4,644,101, issued Feb. 17, 1987 to S. Jin et al.
As compared with single-particle bridging, the use of conductive chains is advantageous for interconnection between uneven surfaces or contact structures because chains may be compressed or bent to accommodate differences in surface distance. Where such differences are of no concern, bridging may be preferred because of its freedom from additional internal contact surfaces, resulting in optimally low contact resistance. With respect to such single-particle, bridging interconnection there remain concerns, however, with the distribution of particles in a layer medium so as to prevent particle agglomerations as well as voids, the former leading to electrical shorting, and the latter to high contact resistance or even complete failure of contact.